This invention relates to a metal member having a metal oxide film and a method of manufacturing the same and, in particular, relates to a metal member having a metal oxide film suitable for use in a manufacturing apparatus used in a manufacturing process of an electronic device such as a semiconductor device or a flat panel display device, and to a method of manufacturing the same.
As manufacturing apparatuses for use in the fields of manufacturing electronic devices such as semiconductor devices or flat panel display devices, use is made of, for example, thin-film forming vacuum apparatuses for use in chemical vapor deposition (CVD), physical vapor deposition (PVD), vacuum evaporation, sputtering, microwave-excited plasma CVD, and so on, dry etching apparatuses for use in plasma etching, reactive ion etching (RIE), recently-developed microwave-excited plasma etching, and so on (hereinafter collectively referred to as vacuum apparatuses), cleaning apparatuses, sintering apparatuses, heating apparatuses, and so on. In recent years, as structural materials of the above-mentioned apparatuses, in particular, as structural materials having surfaces brought into contact with corrosive fluids, radicals, or irradiated ions, lightweight and strong metals containing aluminum as a main component have been widely used instead of stainless steel materials. In order to realize future high-efficiency multi-kind small-quantity production, these apparatuses are required to shift to a three-dimensional cluster tool capable of carrying out a plurality of processes by the single tool, to carry out a plurality of processes by switching the kind of gas in a single process chamber, or the like. Among practical metals, aluminum belongs to a particularly base group and, therefore, aluminum or a metal containing aluminum as a main component requires a protective film formed by an appropriate surface treatment.
As a surface protective film when a metal containing aluminum as a main component is used as a structural material, there is conventionally known an anodized film (alumite) obtained by anodic oxidation or anodization in an electrolyte solution. If an acidic electrolyte solution (normally pH 2 or less) is used as the electrolyte solution, it is possible to form a smooth and uniform alumite coating film having a porous structure.
Further, the alumite coating film is corrosion-resistant and the acidic electrolyte solution is stable and easy to manage. Therefore, the alumite coating film is generally and widely used. However, the alumite coating film having a porous structure is weak against heat as a surface treatment of a structural member and thus causes cracks due to a difference in thermal expansion coefficient between the aluminum base member and the alumite coating film (Patent Document 1—Japanese Unexamined Patent Application Publication (JP-A) No. H10-130884), thereby causing generation of particles, occurrence of corrosion due to exposure of the aluminum base member, and so on.
Further, a large amount of water and so on are accumulated/adsorbed in holes of the porous structure (Patent Document 2-Japanese Examined Patent Application Publication (JP-B) No. H5-053870) and released as a large quantity of outgas components. This causes many problems such as a significant degradation in performance of a vacuum apparatus, operation failure of devices to be manufactured, occurrence of corrosion of the alumite coating film and the aluminum base member due to coexistence with various gases including a halogen gas and chemicals, and so on. Among halogen gases, particularly, a chlorine gas is used as an etching gas in processing, such as reactive ion etching (RIE), of a metal material and is also used in a cleaning process of a thin film forming apparatus or a dry etching apparatus. Therefore, it is important to achieve a metal surface treatment of an apparatus member that can ensure strong corrosion resistance against the chlorine gas.
In terms of this, there are various proposals for alumite coating films with a low increase rate of cracks caused by a high-temperature heat load as well as methods of forming the alumite coating films. For example, there is proposed a method of forming an alumite coating film with a controlled aluminum alloy composition (Patent Document 3—Japanese Unexamined Patent Application Publication (JP-A) No. H11-181595). However, this alumite coating film also has a porous structure on the surface, like the conventional one. Therefore, various problems due to water remaining in holes of the porous structure remain outstanding.
Various methods are proposed for solving the problems caused by this porous structure. For example, there are proposed a sealing treatment in which an alumite coating film with a porous structure anodized in an acidic electrolyte is immersed in boiling water or treated in pressurized steam, thereby forming aluminum hydroxide (boehmite layer) on the surface to seal the holes (Patent Document 4—Japanese Unexamined Patent Application Publication (JP-A) No. H5-114582), a sealing treatment in a solution containing a hydrate or hydrated oxide of a metal as a main component (Patent Document 5—Japanese Unexamined Patent Application Publication (JP-A) No. 2004-060044), and so on. However, water still remains in the holes of the porous structure even after the sealing treatment. The boehmite layer of aluminum hydroxide itself is also a hydrate and thus serves as a water source depending on conditions such as a pressure and a temperature. Thus, a radical solution has not yet been reached. There is also proposed a method of performing anodic oxidation of a barrier structure after forming an alumite coating film of a porous structure (Patent Document 6—Japanese Unexamined Patent Application Publication (JP-A) No. 2005-105300). However, since anodic oxidation in two steps is required, there is a problem that the manufacturing cost increases.
Besides, as a surface treatment when a metal containing aluminum as a main component is used as a structural member, use is made of a thermal spraying method that melts and sprays a powder material of a metal, an alloy, a ceramic, or a combination of the ceramic and the metal or the alloy (Patent Document 7—Japanese Unexamined Patent Application Publication (JP-A) No. H9-069514). However, the surface treatment by the thermal spraying method is still disadvantageous in the following respect. In this method, it is difficult to suppress formation of pores through which the film surface and the base member communicate with each other. Therefore, when a corrosive gas such as a halogen gas is used in an apparatus, the base member is partly corroded at portions where the metal containing aluminum as a main component is brought into contact with the corrosive gas through the pores.